Mitochondria are the site of the essential process of respiration in eukaryotic cells, and contain DNA separate from the nucleus, which encodes only some of the genes needed for mitochondrial function. Mitochondrial gene sequence mutations and deletions have been linked with various human diseases, including cardiomyopathy, neuropathy and various aging disorders. In plants, mitochondrial genome alterations are associated with cytoplasmic male sterility, which results in abortive pollen production. Our long-term goals are to understand the relationship between mitochondrial genome recombination and genome maintenance and repair, and resulting effects on mitochondrial function. We have chosen Arabidopsis thaliana as a model system for these studies, as the complete genome (nuclear, mitochondrial and chloroplast) is now available, propagation of this plant is easy and generation time is short, and genetic studies are possible with this species. Our immediate goals are to identify and characterize genes for mitochondria-targeted recombination proteins in A. thaliana, and characterize the gene products. Homologues of the E. coli rec A and ssb genes, which have mitochondrial targeting sequences, will initially be studied. We have obtained clones of these genes, and their expression will be analyzed in various tissues and ages of plants by northern and western blot analysis to determine if there are spatial or developmental differences in expression of these genes. The effect of over expression of the recA or ssb genes, driven either by global or tissue-specific strong promoters, will be determined in transgenic Arabidopsis plants. Disruption of the endogenous genes by gene knockout or antisense technology will also be examined to determine if mitochondrial DNA recombination is essential for proper I growth and development, and if gene disruption leads to greater susceptibility to DNA damaging agents. Additional Arabidopsis genes with predicted mitochondrial targeting sequences for proteins involved in recombination will be identified and like wise characterized. Our findings will provide greater insights into processes affecting mitochondrial genome integrity, which may be extended to mitochondria from other eukaryotes. [unreadable] [unreadable]